This invention generally relates to slide gate valves for regulating a flow of molten metal, and is specifically concerned with a replaceable refractory valve plate assembly for facilitating maintenance operations for gate valves of the type comprising: a metallic frame mounted on a metallurgical vessel, such as a steel convertor, at least one fixed refractory plate having at least one flow opening, at least one movable refractory plate having at least one flow opening, at least one pouring nozzle firmly connected to the movable plate, means for controlling the displacement of the movable plates with respect to the fixed plate in order to control the overlap of the flow openings of the two plates; and compression means for forcefully engaging the movable plate against the fixed plate to provide a fluid seal therebetween.
In a device of this type the metal parts of the slide gate valve, particular the metal frame or housing, generally have a service life of several hundred or even several thousand tappings of the molten metal. By contrast, the flow-regulating refractory components (i.e., the fixed plate, the movable plate, and pouring nozzle) have a service life of only a small number of tappings, and thus must be replaced frequently.
Two methods are currently employed to replace these refractory components:
According to a first method, each refractory component is replaced individually. In certain configurations the pouring nozzle is accessed from outside the metal frame, but it is necessary to open the frame in order to gain access to the refractory plates. For example, the slide gate valve may have a door or the like mounted on hinges, which door can be opened to gain access to the refractory components. Each worn refractory plate is removed individually and replaced by a new refractory plate, which may or may not be covered with a metal shell. This method is satisfactory when the refractory components to be manipulated are light enough to be replaced manually and are accessible under environmental conditions which allow the operator to have easy access without danger. However, in the case of large slide gate valves, such as those used for steel furnaces, converters, or large ladles or tundishes, each refractory component may weigh hundreds of pounds. In the case of furnaces or converters (which, in contrast to ladles, tundishes and the like, cannot be transported away from their operating environment), the refractory components must be replaced in situ under conditions which themselves impose a stress on an operator, particularly with regard to heat. These conditions are aggravated in that the slide gate valve cannot be adequately cooled due to the constraint of keeping plate replacement time to a minimum, since production must be interrupted during this time and thus losses must be suffered. The conditions imposed on the operator are thus particularly arduous. It is conceivable to aid the operator with implements such as robots or manipulators. For such implements, the weight of the plates is not an obstacle. However, a crucial factor lies in the number of operations to be carried out. The time required to replace the plates with the aid of a manipulator or robot will be much greater than that required for an operator to perform the same replacement manually. Each gripping implement must be adapted to the object to be manipulated. A solution of this nature will thus be very costly, complex and time-consuming.
According to a second known method, the entire slide gate valve is removed from the vessel and replaced by a new slide gate valve containing new refractory components. This method also has a number of drawbacks. The complete slide gate valve weights much more than the refractory components to be replaced, e.g. 20 times more. Thus, if the refractory components weight 100 kg, it is necessary to manipulate other components weighing 2000 kg, which requires powerful implements and very long manipulation times. Under the second method, it is also necessary to disconnect and reconnect the pneumatic cylinder or the like which slides the movable plate back and forth, and to remove and reattach various protective shields that surround the valve. The total time required and the number of operations required are considerable. Moreover, the slide gate valve containing the worn refractory components must be transported to a shop where the worn refractory components are replaced by new ones. While the working conditions are less stressful, particularly as regards to heat, and the time factor is less critical because production need not be interrupted during this refitting the number of operations necessary to replace the refractory elements remains the same, and the cost of the transportation means and the shop must be borne.